Category · F40-F48 block
F43 — Reaction to severe stress, and adjustment disorders
Terminology note: This category is organised around a duration and severity gradient following an identifiable stressful or traumatic event: acute stress reaction (hours to days, following an exceptionally severe stressor), post-traumatic stress disorder (weeks to months or longer, following an exceptionally threatening or catastrophic event, with a characteristic re-experiencing/avoidance/hyperarousal symptom cluster), and adjustment disorder (a milder, more varied reaction to a significant life change or stressor that need not be exceptionally traumatic).
What is this category?
F43 covers presentations that arise as a direct reaction to an identifiable stressful or traumatic event, distinguished from one another chiefly by the severity of the precipitating stressor, the characteristic symptom cluster, and the timescale over which the reaction unfolds.
Core diagnostic concept
All three main F43 subtypes require an identifiable precipitating stressor or event — this category does not apply to anxiety or mood disturbance that arises without one. What separates the subtypes is the severity of that stressor (exceptionally catastrophic versus a significant but ordinary life change), the specific symptom cluster (PTSD's characteristic re-experiencing, avoidance, and hyperarousal versus a more varied emotional and behavioural reaction), and the timescale (hours-to-days for acute stress reaction, weeks-to-months-or-longer for PTSD, and typically within one month of the stressor, resolving within six months of it ending, for adjustment disorder).
Key diagnostic features
- Identifiable precipitating stressor required
- All three main subtypes require a clear temporal and causal link to an identifiable stressful or traumatic event.
- Severity of stressor differentiates PTSD from adjustment disorder
- PTSD requires an exceptionally threatening or catastrophic event; adjustment disorder can follow a significant but non-catastrophic life change or stressor.
- Characteristic symptom cluster for PTSD
- Re-experiencing (intrusive memories, flashbacks, nightmares), avoidance of reminders, and persistent hyperarousal together, not any one alone.
- Timescale differentiates acute stress reaction from PTSD
- Acute stress reaction resolves within hours to days; PTSD symptoms persist for weeks, months, or longer.
How to weigh evidence
These learning labels are teaching aids, not official ICD-10 terminology (see Sources and Method).
- supports A clear precipitating stressor followed, on an appropriate timescale, by the characteristic symptom cluster for the subtype in question.
- consistent not decisive General distress following a difficult life event, without yet enough detail on duration or the specific symptom cluster to assign a subtype.
- raises alternative Anxiety or low mood that appears unrelated to any identifiable stressor, or that clearly predates the stressor in question.
- contradicts or weakens Symptoms that have already resolved within days, arguing against ongoing PTSD; or a stressor that was not exceptionally catastrophic, arguing against PTSD in favour of adjustment disorder.
- missing and necessary to ask The exact timescale since the stressor, whether the characteristic PTSD symptom cluster (re-experiencing, avoidance, hyperarousal) is present, and the severity of the precipitating event.
Diagnostic boundary
F43 requires a reaction to an identifiable stressful or traumatic event; which subtype applies depends on the stressor's severity, the specific symptom cluster present, and how much time has elapsed since the event.
Full comparisons:
Duration and course
Minimum duration: Acute stress reaction: hours to a few days. PTSD: typically weeks or more following the trauma, sometimes with delayed onset. Adjustment disorder: onset within about one month of the stressor, usually resolving within six months unless the stressor persists.
Course: Each subtype's course is part of what defines it, not incidental detail.
Included presentations
- Acute stress reaction: a transient reaction, hours to days, to an exceptionally severe physical or psychological stressor.
- Post-traumatic stress disorder: a characteristic cluster of re-experiencing, avoidance, and hyperarousal symptoms, persisting for weeks or longer, following an exceptionally threatening or catastrophic event.
- Adjustment disorder: a milder, more varied emotional or behavioural reaction to a significant life change or stressor, arising within about a month of it.
Exclusions and distinguishing presentations
| If this is true instead… | Consider | Why |
|---|---|---|
| Anxiety or low mood with no identifiable precipitating stressor | F41 | F43 specifically requires an identifiable stressful or traumatic event as the precipitant. |
| Dissociative symptoms (e.g. amnesia, altered sense of identity) becoming the predominant presentation rather than a secondary feature of a stress reaction | F44 | When dissociative symptoms become the predominant, defining feature rather than one feature among a broader stress-reaction symptom cluster, F44 becomes the more accurate primary classification. |
Four-character subtypes (orientation)
A learner should check the stressor's severity, the specific symptom cluster present, and the timescale together — a recent, non-catastrophic stressor with a milder reaction supports adjustment disorder, not PTSD, however distressing it is for the person.
- F43.0 — Acute stress reaction
- A transient reaction, hours to days, to an exceptionally severe stressor. (in_depth)
- F43.1 — Post-traumatic stress disorder
- Characteristic re-experiencing, avoidance, and hyperarousal, persisting for weeks or longer, following a catastrophic event. (in_depth)
- F43.2 — Adjustment disorders
- A milder, more varied reaction to a significant life change or stressor, within about a month of it. (in_depth)
- F43.8 — Other reactions to severe stress
- A stress-reaction presentation not matching the named subtypes. (taught for orientation only, not separately assessed in this pilot)
- F43.9 — Reaction to severe stress, unspecified
- A stress reaction identified but without enough information to specify further. (taught for orientation only, not separately assessed in this pilot)
External causes to check first
Categories in this block require that the disturbance is not better explained by another external cause listed below. These short capsules are reminders, not full teaching modules.
External cause capsule — Organic, medical, or substance-related presentations resembling F40-F48
A reminder that a presentation resembling an anxiety, obsessive-compulsive, stress-related, dissociative, or somatoform disorder can instead be caused by a general medical condition (e.g. hyperthyroidism producing anxiety-like symptoms, a neurological condition producing genuine sensory or motor loss) or a substance/medication (e.g. caffeine or stimulant intoxication, sedative or alcohol withdrawal producing anxiety symptoms) rather than being a primary F40-F48 disorder, and that this should be actively considered before a primary F40-F48 classification is settled.
What to check:
- Timing: did the symptoms begin during or shortly after starting, stopping, intoxication with, or withdrawal from a substance or medication known to produce anxiety, dissociative, or somatic symptoms?
- Medical context: is there a known medical or neurological condition (e.g. thyroid disease, a cardiac arrhythmia, a neurological lesion) with a recognised association with the symptoms described?
- Adequacy of investigation: has an appropriate medical or neurological work-up actually been completed, rather than simply not yet undertaken?
- Course after the cause is addressed: symptoms that substantially improve once the medical condition is treated or the substance/medication is stopped weigh toward a secondary cause rather than a primary F40-F48 disorder.
A full teaching module on F00-F09 (organic mental disorders) or F10-F19 (substance-related disorders), or a general medical work-up, all of which are outside this capsule's scope.
Worked example — distinguishing PTSD from adjustment disorder
Six weeks after surviving a serious road traffic collision in which a passenger was killed, a 41-year-old reports vivid, intrusive flashbacks of the crash several times a week, avoids driving or being a passenger in any vehicle, startles severely at sudden sounds, and has not slept through a night since. He describes feeling emotionally numb and detached from his family.
- Step 1 — Identify the stressor: a serious road traffic collision involving a fatality — an exceptionally threatening and catastrophic event.
- Step 2 — Check for re-experiencing: vivid, intrusive flashbacks several times a week.
- Step 3 — Check for avoidance: avoiding driving or being a passenger in any vehicle.
- Step 4 — Check for hyperarousal: severe startle response, poor sleep.
- Step 5 — Check timescale: six weeks, well beyond acute stress reaction's hours-to-days window, with the full characteristic symptom cluster present.
- Conclusion — F43.1, Post-traumatic stress disorder — an exceptionally catastrophic stressor, the full re-experiencing/avoidance/hyperarousal cluster, and a persisting timescale together support PTSD over acute stress reaction or a milder adjustment disorder.
Interactive practice
- Type A Six weeks after the collision Recognition / application · Foundation
- Type B Shaken up, but already settling Boundary discrimination · Developing
- Type C Two days out — too soon to tell Insufficient information · Developing
Retrieval prompts
Try answering each of these from memory before revealing where to check. Nothing you think or type here is sent or saved anywhere.
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Name the three features that together make up PTSD's characteristic symptom cluster.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
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State the approximate timescale that separates acute stress reaction, PTSD, and adjustment disorder.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
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Explain why adjustment disorder does not require an exceptionally catastrophic stressor.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
These self-checks are a personal study aid only, visible to you on this page for this visit — they are not stored and do not affect your mastery dimensions.
Rapid revision card
F43: F43 requires a reaction to an identifiable stressor; severity of the stressor, the specific symptom cluster, and timescale together decide which subtype applies.
Decisive boundary cues:
- Hours-to-days, following an exceptionally severe stressor -> acute stress reaction.
- Weeks or longer, with re-experiencing + avoidance + hyperarousal, following a catastrophic event -> PTSD.
- A milder, more varied reaction within about a month of a significant but non-catastrophic life change -> adjustment disorder.
Duration/course: Acute stress reaction: hours-days. PTSD: weeks or longer. Adjustment disorder: within about a month of onset, usually resolving within six months.
Nearest alternatives: f41, f44
Common mistake: Assuming any distressing life event automatically supports PTSD, without checking the stressor's severity and the specific re-experiencing/avoidance/hyperarousal symptom cluster.
Retrieval prompt: How severe was the stressor, what is the specific symptom cluster present, and how much time has elapsed since the event?
(or use your browser's print function) Open full-page printable revision view →
Source basis
WHO ICD-10 international classification structure and code/title (ICD-10 Browser, 2019 English release).
Original educational synthesis, informed by general published clinical-education understanding of ICD-10 F40-F48; no verbatim CDDG or DCR text is reproduced. See Sources and Method for the full policy.
Last reviewed: 2026-09-16. Full policy: Sources and Method.
Educational resource only. This page and its cases teach ICD-10 classification reasoning using fictional scenarios. It does not diagnose real people and should not be used to assess yourself or anyone else. If you or someone you know is struggling with anxiety, intrusive thoughts, the effects of a stressful or traumatic event, or persistent physical symptoms, please seek prompt professional evaluation.